1. Field of the Invention
This invention relates to improvements in the preparation of concrete and is more particularly concerned with incorporating polyisocyanate compositions into concrete to improve the properties thereof.
2. Description of the Prior Art
A variety of aqueous compositions derived from polyisocyanates is known in the art. Illustratively, aqueous emulsions, derived from polyisocyanates having all the isocyanate groups blocked by capping agents such as phenol, are described in U.S. Pat. Nos. 3,499,824; 3,933,677; 3,996,154 and 3,997,592. Water soluble solutions of the bisulfite complexes of blocked polyisocyanates and bisulfite-blocked isocyanate-terminated prepolymers are described in U.S. Pat. Nos. 3,483,189 and 3,984,365, respectively. Aqueous emulsions derived from solutions of polyisocyanates in dimethylformamide and like alkylated amides are described in U.S. Pat. No. 3,428,592.
U.S. Pat. No. 3,410,817 describes a polyurethane latex obtained by making an aqueous emulsion of an isocyanate-terminated prepolymer (optionally in the presence of a chain extender) and then precipitating the emulsion by addition of an alcohol.
U.S. Pat. No. 3,897,581 relates to the use of certain isocyanate-terminated prepolymers as water-curable adhesives for bonding of plywood and the like. Certain of the isocyanate-terminated prepolymers specifically described and exemplified are said to be soluble in water and to react therewith.
While it has been suggested that aqueous compositions of the above type can be used as sealing compositions for coating concrete and the like, it has not been suggested previously that such compositions should be incorporated into concrete during the formation thereof.
We have now found that certain novel homogeneous aqueous solutions can be incorporated into concrete during its formation and that the concrete so produced has markedly improved structural strength and other properties which will be described hereafter.